Fluorinated polymer films, such as PTFE (polytetrafluoroethylene) and related polymer coatings may be produced by hot filament chemical vapor deposition (HFCVD), initiated chemical vapor deposition (iCVD), or other vapor phase deposition processes. While these coatings possess many desirable properties, they sometimes do not fulfill all the requirements of certain applications. For example, conventional iCVD PTFE is a fairly soft coating which may not provide adequate levels of mechanical durability for some applications. Further, the adhesion of PTFE to some surfaces requires improvement. Attempts to improve the mechanical properties and adhesion of iCVD PTFE by varying process conditions, film chemistry, and surface treatment techniques has proved challenging due to the non-polarity and chemical inertness of PTFE's polymeric backbone. Accordingly, new methods for forming coatings with improved mechanical properties are needed.
While PTFE is a fairly lubricious coating, PTFE polymeric chains produced by iCVD may have polar end groups, reducing the coating's lubricity and overall stability. High lubricity is useful for applications where one coated surface needs to slide over another while the two are in physical contact (e.g., a stopper sliding over the surface of a syringe barrel). Accordingly, methods of eliminating polar end groups on PTFE chains and improving the lubricity of PTFE coatings would be useful.
During iCVD or HFCVD of coatings, heated filaments used to decompose process gases can also degrade temperature sensitive articles (e.g., polymeric medical articles). Examples of such articles include elastomeric seals, which may subsequently be incorporated into medical devices or semiconductor processing equipment or aerospace platforms. The coatings may be polymeric or non-polymeric. To accommodate these temperature sensitive articles, methods for cooling the article during coating deposition would be useful.
For other applications, it may be desirable to raise the temperature of an article during coating deposition. At low temperatures, articles may be coated with an undesirable proportion of low-molecular-weight polymeric chains using iCVD, adversely impact the articles' performance in some applications. Raising the temperature of the articles during coating discourages the adsorption of these low-molecular-weight chains.
Typically, conventional CVD equipment employs flat sample stages whose geometry may not be complementary to that of the articles being coated. Many polymeric articles, for example, exhibit low thermal conductivities and have complex shapes. Therefore, even if these conventional stages were heated or cooled, the temperature of polymeric articles with complex shapes may not be adequately controlled. As a result, the articles may still either be thermally degraded by the heated filaments or be coated with a coating that exhibits undesirable performance. Accordingly, new methods for the temperature control of substrates are required.
Thermal damage to low-temperature articles can be exacerbated by in-service deformation of the heated filaments. Deformation may be initially caused by filament stretching and later by out-of-plane filament bowing when the filament is heated to coating deposition temperatures. The filament may bow toward the parts being coated. In addition to damaging the articles themselves, increased proximity of the hot filament to the articles may discourage adsorption and growth of the polymer coating being deposited. As such, the coating deposition rates may drop to levels that are intolerable in a high-volume manufacturing environment. Means of detecting and preventing filament deformation are required so as to minimize any negative impact of such deformation on the coating deposition process. The filament replacement schedule that is typical of hot-filament CVD processes (e.g., due to filament aging, deformation, or breakage) may also require prohibitively-long production delays. Means of shortening these delays would be useful.